# Correlation Between Psoas and Diaphragmatic Ultrasound Indices for the Assessment of Sarcopenia in Patients with Inflammatory Bowel Disease: A Prospective Single-Center Study

## TL;DR

This study explores the use of diaphragm ultrasound as a practical alternative to psoas muscle measurements for assessing sarcopenia in inflammatory bowel disease patients.

## Contribution

The study demonstrates a significant correlation between diaphragm and psoas ultrasound indices, suggesting the diaphragm as a feasible sarcopenia marker in IBD.

## Key findings

- Diaphragm thickness showed a moderate positive correlation with psoas-to-height ratio (r = 0.3568, p < 0.05).
- Bland–Altman analysis confirmed a symmetrical distribution between diaphragm and psoas indices.
- Multivariable regression showed the diaphragm index increased linearly with psoas-to-height ratio (β = 0.018, p = 0.008).

## Abstract

Background and Aim: Sarcopenia is increasingly recognized as a clinically significant complication of inflammatory bowel disease (IBD), influencing both medical management and surgical outcomes. Accurate and accessible diagnostic tools are essential for assessing muscle mass and function in this population. The iliopsoas (IP) muscle has traditionally been used as a marker of sarcopenia, but its deep anatomical location requires skilled operators. Conversely, the diaphragm (DM), being more superficial, may serve as a more feasible surrogate. This study aimed to assess the correlation between IP- and DM-derived ultrasound indices in patients with IBD and to explore their association with sarcopenia risk. Methods: This prospective single-center study enrolled 353 IBD patients (Crohn’s disease [CD] and ulcerative colitis [UC]). Overall, 57 patients had a SARC-F score ≥ 4 and underwent intestinal ultrasound (US). The transverse diameter of the right IP muscle was measured in triplicate, and the psoas-to-height ratio (PMTH, mm/m) was calculated. Diaphragm thickness was assessed during inspiration and expiration, and the diaphragm-to-height ratio was derived. Pearson correlation, Bland–Altman analysis and multivariable regression (adjusted for age and sex) were performed to test associations. Results: The mean IP diameter was 28.40 mm (28.82 mm in males, 27.02 mm in females), with a mean PMTH of 16.62 mm/m. Diaphragm thickness was 20.4 ± 5.0 mm at inspiration and 10.7 ± 3.5 mm at expiration, yielding a mean difference of 9.7 ± 3.4 mm. The diaphragm-to-height ratio was 0.59 ± 0.21 mm/m. Pearson correlation revealed a moderate positive association between PMTH and the diaphragm index (r = 0.3568, p < 0.05). Bland–Altman analysis disclosed a symmetrical distribution. Multivariable regression confirmed that the diaphragm index increased linearly with PMTH (β = 0.018, 95% CI 0.005–0.030; p = 0.008). Neither age nor sex significantly affected the results. Conclusions: Muscle ultrasound is a reliable and reproducible method for evaluating sarcopenia in IBD. The diaphragm, due to its superficial anatomical location and ease of measurement, shows a significant correlation with psoas muscle parameters and may serve as a practical surrogate marker in clinical practice. Larger multicenter studies are warranted to validate these findings.